Microelectronic structure

ABSTRACT

A microelectronic structure is described which contains a first conductive layer for preventing oxygen diffusion at the structure. The first conductive layer contains a base material and at least one oxygen-binding admixture that is provided with at least one element from the fourth subgroup or the lanthane group. In a preferred embodiment, the microelectronic structure is used in semiconductor storage components with a metal oxide dielectric as a condenser dielectric.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of copending InternationalApplication No. PCT/DE99/03832, filed Dec. 1, 1999, which designated theUnited States.

BACKGROUND OF THE INVENTION

[0002] Field of the Invention

[0003] The invention is in the field of semiconductor technology andrelates to a microelectronic structure which has at least one substrateand one first conductive layer. Microelectronic structures such as theseare used in particular in semiconductor memories.

[0004] Materials having a high dielectric constant (Epsilon>20) orhaving ferroelectric characteristics are being increasingly used inorder to further increase the integration density in semiconductormemories. Those materials which are of major interest at the moment aremetal oxide dielectrics, which are deposited at relatively hightemperatures in the presence of oxygen. Prominent representatives are,for example, barium-strontium-titanate ((Ba,Sr)TiO₃, BST),lead-zirconate-titanate (PbZrTiO₃, PZT), strontium-bismuth-tantalate(SrBi₂Ta₂O₉, SBT) and derivatives of the above mentioned materials. Thehigh deposition temperatures required and the oxygen atmosphere that ispresent pose stringent requirements on the already formed structures onthe semiconductor substrates, in particular on the lower electrode ofthe storage capacitor and on any barrier layer located under theelectrode. Oxygen-resistant noble metals, in particular, have beenproposed as electrode materials. Since noble metals such as these, inparticular the preferred platinum, form interfering metal suicides withsilicon, a barrier layer which is normally disposed between theelectrode and the silicon substrate or polysilicon layer is intended toprevent the silicon from diffusing into the platinum electrode. Thebarrier layer is formed of titanium or a titanium-titanium nitride.

[0005] However, this has the disadvantage that the titanium oxidizesrelatively quickly at relatively high deposition temperatures (above500° C.) and in consequence prevents a conductive connection from beingformed between the electrode and the silicon. A range of measures havethus been proposed in order to protect the barrier layer againstoxidation during the deposition of the metal oxides.

[0006] One option is, for example, to bury the barrier in anoxygen-resistant nitride layer, and this is proposed, for example, inU.S. Pat. No. 5,619,393. In this solution, the barrier layer issurrounded in the form of a collar by the nitride layer, and its upperface is completely covered by the electrode, which extends to beyond thecollar. However, production of such a structure involves a relativelylarge number of process steps. A further option of avoiding the problemof oxidation of the barrier layer is to use a structure in which theupper electrode, rather than the lower electrode, is connected via aconductive layer to the associated selection transistor. This makes itpossible to dispense with a conductive barrier layer underneath thelower electrode. However, the structure, which is described, forexample, in U.S. Pat. No. 5,122,477, has the disadvantage that itoccupies a relatively large amount of space and is thus unsuitable forvery large scale integrated memory components.

SUMMARY OF THE INVENTION

[0007] It is accordingly an object of the invention to provide amicroelectronic structure which overcomes the above-mentioneddisadvantages of the prior art devices of this general type, whichallows simple and reliable protection of an oxygen-sensitive layer, andto specify a method for producing such a structure.

[0008] With the foregoing and other objects in view there is provided,in accordance with the invention, a microelectronic structure. Themicroelectronic structure contains at least one substrate and a firstconductive layer disposed on the substrate. The first conductive layeris composed of at least one basic material having at least oneoxygen-bonding additive containing at least one element selected fromthe group consisting of Group IVb elements and lanthanum group elements.A second conductive layer is disposed on the first conductive layer andcontains a noble metal. A metal oxide dielectric at least partiallycovers the second conductive layer.

[0009] The object is achieved according to the invention in the case ofa microelectronic structure of the type mentioned initially by the firstconductive layer being composed of at least one basic material having atleast one oxygen-bonding additive, which contains at least one elementfrom Group IVb or from the lanthanum group.

[0010] The basic idea of the invention is to provide a conductive layerwith suitable oxygen-bonding additives. These are intended to preventdiffusion of oxygen and/or of oxides which assist diffusion, and thus toprotect those structures which are located under the conductive layeragainst oxidation. To this end, the first conductive layer is composedof at least one basic material which is electrically conductive and, isvery largely oxygen-resistant, and in which the oxygen-bonding additiveis distributed as uniformly as possible. The important feature is thatthe oxygen-bonding additive is present even before the action of theoxygen on the structures to be protected in the basic material and thusprevents oxygen diffusion through the first conductive layer.

[0011] Normally, the at least one oxygen-bonding additive forms an alloyor a mixed layer with the basic material, which may be formed of one ormore components, in which case the oxygen-bonding additive may also atleast partially be present in the form of a finely distributed depositin the basic material. The advantages of a uniform distribution of theoxygen-bonding additive are, in particular, the uniform oxygenresorption capability of the first conductive layer, the adaptation ofthe resorption capability by variation of the layer thickness of thefirst conductive layer and a uniform and very largely stress-freeincrease in volume due to the oxygen bonding.

[0012] Elements from Group IVb and from the lanthanum group have beenfound to be particularly advantageous as oxygen-bonding additives, withzirconium, hafnium, cerium or a combination of the elements beingparticularly preferred. It is also advantageous for the oxygen-bondingadditive to be added to the basic material with a proportion by weightof between 0.5% and 20%, preferably of between 1% and 10%.

[0013] Suitable basic materials for the first conductive layer are noblemetals, in particular platinum, palladium, rhodium, iridium, ruthenium,osmium, rhenium, conductive oxides of the abovementioned metals or amixture of the abovementioned compounds and elements.

[0014] It is also preferable for the microelectronic structure to have ametal oxide dielectric that at least partially covers the firstconductive layer. The metal oxide dielectric is used, in particular insemiconductor memories, as a capacitive dielectric, with the firstconductive layer being at least part of one electrode of the storagecapacitor. Since the metal oxide dielectric is normally applied directlyto the first conductive layer, any barrier layer which is preferablylocated underneath the first conductive layer must be protected againstattack by oxygen while it is being deposited in an atmosphere containingoxygen.

[0015] The metal oxide dielectric preferably contains a compound of thegeneral nature ABO, where O represents oxygen, and A and B eachrepresent at least one element in the group containing barium,strontium, tantalum, titanium, lead, zirconium, niobium, lanthanum,calcium and potassium. The general compound ABO often has a crystalstructure similar to perovskite, which is a critical factor for thedesired dielectric (high dielectric constant) characteristics or for theferroelectric characteristics. One example of such a compound isSrBi₂Ta₂O₉.

[0016] A second conductive layer, which preferably contains a noblemetal, in particular platinum, is preferably disposed between the firstconductive layer and the metal oxide dielectric in order to improve theelectrical characteristics of the metal oxide dielectric. The additionalconductive layer first represents an inert and smooth boundary surfacefor the growth of the metal oxide dielectric, and second assists thecrystal growth of the metal oxide dielectric during its deposition andduring subsequent heat treatment and, furthermore, provides additionaloxidation protection.

[0017] The bonding capacity of the first conductive layer with regard tooxygen should be set as appropriate by choice of the amount of additive,so that no further additional layers to prevent oxygen diffusion arerequired. An additive level of between 8 and 10%, for example, issufficient to prevent the oxygen diffusion, which occurs duringdeposition and heat treatment of the metal oxide dielectrics, throughthe first conductive layer, whose thickness is about 100 nm, virtuallycompletely. The first conductive layer may thus be thinner, in order tosave costs.

[0018] In accordance with an added feature of the invention, a barrierlayer is disposed between the first conductive layer and the substrate.

[0019] In accordance with an additional feature of the invention, thebarrier layer contains titanium.

[0020] With the foregoing and other objects in view there is furtherprovided, in accordance with the invention, a method for producing themicroelectronic structure. The method includes the steps of preparing asubstrate, and simultaneously applying a basic material and aoxygen-bonding additive to the substrate to form a first conductivelayer. The oxygen-bonding additive contains at least one elementselected from the group consisting of Group IVb elements and lanthanumgroup elements. A second conductive layer is deposited onto the firstconductive layer, the second conductive layer contains a noble metalsuch as platinum. Finally, a metal oxide dielectric is applied to thesecond conductive layer.

[0021] The second part of the object is achieved by the method forproducing a microelectronic structure which has at least one substrateand a first conductive layer, with the first conductive layer beingcomposed of at least one basic material having at least oneoxygen-bonding additive which contains at least one element from GroupIVb or from the lanthanum group. The method includes the steps ofpreparing a substrate, the simultaneous application of the basicmaterial and of the oxygen-bonding additive to the substrate in order toform the first conductive layer.

[0022] In the method, the basic material and the oxygen-bonding additiveare preferably applied to the substrate at the same time, so that thefirst conductive layer is formed there as a mixture of the basicmaterial and of the oxygen-bonding additive. If the depositiontemperatures and the additive level of the oxygen-bonding additive areselected appropriately, the latter can at least partially be depositedfrom the basic material, or can form a mixed crystal together with thebasic material.

[0023] It is advantageous to apply the basic material and theoxygen-bonding additive to the substrate by a physical sputteringmethod. This is preferably done using a common source for the basicmaterial and the oxygen-bonding additive, with this being achieved in asimple manner by a sputtering target which consists of the basicmaterial and has wafers which contain the oxygen-bonding additiveapplied to it. Therefore, there is no need to provide a mixed source. Infact, it is easy to vary the nature of the oxygen-bonding additive andits additive level.

[0024] By way of example, a pressure of about 0.02 mbar and a substratetemperature of about 200° C. are preferably used for producing aniridium layer with an oxygen-bonding hafnium additive.

[0025] In accordance with an added mode of the invention, there is thestep of applying the basic material and the oxygen-bonding additive tothe substrate by a physical sputtering method using a common source.

[0026] Once the first conductive layer has been applied, the metal oxidedielectric is applied by metal organic chemical vapor deposition (MOCVD)methods or spin-on methods.

[0027] The microelectronic structure is preferably used in a memoryapparatus, with the first conductive layer representing a firstelectrode which, together with a further electrode and the metal oxidedielectric that is disposed between these electrodes, forms a storagecapacitor. A large number of such storage capacitors are preferablydisposed on one substrate.

[0028] Furthermore, the microelectronic structure is generally suitablefor use as an oxygen diffusion barrier, in order to protectoxygen-sensitive areas of the microelectronic structure, in particular asemiconductor structure, against attack by oxygen.

[0029] Other features which are considered as characteristic for theinvention are set forth in the appended claims.

[0030] Although the invention is illustrated and described herein asembodied in a microelectronic structure, it is nevertheless not intendedto be limited to the details shown, since various modifications andstructural changes may be made therein without departing from the spiritof the invention and within the scope and range of equivalents of theclaims.

[0031] The construction and method of operation of the invention,however, together with additional objects and advantages thereof will bebest understood from the following description of specific embodimentswhen read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a diagrammatic, partial, sectional view of a storagecapacitor using a microelectronic structure according to the invention;

[0033]FIG. 2 is a partial, sectional view of a second embodiment of thestorage capacitor;

[0034]FIG. 3 is a partial, sectional view of a third embodiment of thestorage capacitor; and

[0035]FIG. 4 is an illustration of a sputtering reactor for producingthe microelectronic structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] In all the figures of the drawing, sub-features and integralparts that correspond to one another bear the same reference symbol ineach case. Referring now to the figures of the drawing in detail andfirst, particularly, to FIG. 1 thereof, there is shown a storagecapacitor 5 which is disposed on a substrate 10. The storage capacitor 5contains a lower electrode 15, which is formed in layers from an iridiumoxide layer 20, an iridium layer 25 and a platinum layer 30. Optionally,it is also possible to use ruthenium oxide and ruthenium instead ofiridium oxide and iridium. Together, the iridium oxide layer 20 and theiridium layer 25 represent a first conductive layer. At least one of theiridium oxide 20 or iridium layers 25 contains an oxygen-bondingadditive, which is preferably formed by hafnium. Depending on itsadditive level of between 1% and 10%, this can form a mixed crystal withthe respective layer or may be partially present in the form of adeposit.

[0037] The platinum layer 30 represents a second conductive layer in thepresent embodiment. The lower electrode 15, which is formed in layers,was preferably structured by jointly etching the three layers 20, 25 and30. This is done, for example, by an anisotropic etching process with ahigh physical component that is achieved, for example, in an argonsputtering process. Chlorine or hydrogen bromide (HBr) can be added tothe argon plasma to assist the process.

[0038] A barrier layer 35 containing titanium is located underneath thelower electrode 15. It is used to improve the adhesion characteristicsof the lower electrode 15 on the substrate 10, and to prevent silicondiffusion. This is particularly necessary since the lower electrode 15is connected through a contact hole 40 (which is filled withpolysilicon) in the substrate 10 to a selection transistor, which is notillustrated here in any more detail. A barrier layer 35, which is formedof titanium-titanium nitride, is preferably structured jointly togetherwith the lower electrode 15. Therefore, only a single etching step isrequired for the structure containing the lower electrode 15 and thebarrier layer 35.

[0039] The lower electrode 15 is completely covered by a SBT layer 45,with the latter representing a metal oxide dielectric. The SBT layer 45thus also makes direct contact with the edge areas of the barrier layer35. Therefore, these areas are not protected during the deposition ofthe SBT layer 45. However, since the penetration depth of the oxygendiffusion into the barrier layer 35 is limited, the entire barrier layer35 is not oxidized, but only those areas that are directly adjacent tothe SBT layer 45. The central area of the barrier layer 35, which islocated in particular in the area of the contact hole 40, is protectedagainst oxidation by the lower electrode disposed above it and inparticular by the hafnium additive contained in the iridium oxide layer20 or the iridium layer 25. Furthermore, the iridium layer 25 itselfacts as a protective layer, since iridium is at least partially oxidizedin the SBT process conditions (about 800° C., atmosphere containingoxygen), and thus impedes oxygen diffusion.

[0040] After the application of the SBT layer, a further electrode 50 isdeposited over the entire area onto the SBT layer 45. Together with thelower electrode 15 and the SBT layer 45, the further electrode 50 formsthe ferroelectric storage capacitor 5.

[0041] A second embodiment of the structure is illustrated in FIG. 2 andallows the barrier layer 35 to be protected better. In this structure,the platinum layer 30 also covers the side areas of the layer stackcontaining the barrier layer 35, the iridium oxide layer 20 and theiridium layer 25, so that the SBT layer 45 does not make direct contactwith the barrier layer 35. Another advantageous feature of the structureis that the entire boundary surface between the lower electrode 15 andthe SBT layer 45 is formed by the platinum layer 30, and the boundarysurface characteristics and the storage characteristics of the SBT layer45 are thus improved.

[0042]FIG. 3 illustrates a third embodiment of the structure. In thestructure, the barrier layer 35 is formed only in the area of thecontact hole 40, so that the barrier layer 35 is completely covered bythe iridium oxide layer 20. The barrier layer 35 is thus completelyprotected against oxidation during the SBT deposition. Optionally, inthe structure, the platinum layer 30 can also be continued over the sideareas of the iridium oxide layer 20 and of the iridium layer 25, inorder to improve the capacitor characteristics.

[0043] It has been found that the oxygen absorption when using hafniumleads only to a relatively minor increase in the volume of the iridiumoxide layer 20 and of the iridium layer 25, so that any mechanicalstresses which occur in consequence do not lead to damage.

[0044] Reference is made to FIG. 4 in order to illustrate the methodaccording to the invention for producing a microelectronic structure inwhich the first conductive layer is formed of a basic material and anoxygen-bonding additive. A sputtering reactor 55 is illustratedschematically here, having a substrate mount 60 and a target holder 65,which at the same time act as the cathode and anode, respectively. Asilicon wafer 70, which subsequently forms the substrate 10, is locatedon the substrate mount 60. An iridium wafer 75 with hafnium wafers 80placed on it is attached to the target holder 65, which is disposedopposite the silicon wafer 70. Together, the wafers represent the commonsource during the sputtering process. The proportion of hafnium that isdeposited can be set by choice of the wafer size of the hafnium wafer.Hafnium and iridium are precipitated jointly from the respective sourcesby the argon plasma produced in the sputtering reactor 55, and areapplied as a mixture to the silicon wafer 70. It is also possible toreplace the iridium wafer 75 by an iridium oxide wafer.

[0045] In order to improve the adhesion strength of the sputtered layerson the silicon wafer 70, the wafer can be heated by heating applied fromunderneath the wafer. Advantageous temperatures are in the range 200° to500° C.

We claim:
 1. A microelectronic structure, comprising: at least onesubstrate; a first conductive layer disposed on said substrate, saidfirst conductive layer composed of at least one basic material having atleast one oxygen-bonding additive containing at least one elementselected from the group consisting of Group IVb elements and lanthanumgroup elements; a second conductive layer disposed on said firstconductive layer and containing a noble metal; and a metal oxidedielectric at least partially covering said second conductive layer. 2.The microelectronic structure according to claim 1, wherein saidoxygen-bonding additive is selected from the group consisting ofzirconium, hafnium, cerium and a combination of zirconium, hafnium andcerium.
 3. The microelectronic structure according to claim 1, whereinsaid oxygen-bonding additive forms a proportion by weight of said firstconductive layer of between 0.5% and 20%.
 4. The microelectronicstructure according to claim 1, wherein said basic material is a noblemetal selected from the group consisting of platinum, palladium,rhodium, iridium, ruthenium, osmium, rhenium, a conductive oxide of theabovementioned metals, and a mixture of the abovementioned compounds andelements.
 5. The microelectronic structure according to claim 1,including a barrier layer disposed between said first conductive layerand said substrate.
 6. The microelectronic structure according to claim5, wherein said barrier layer contains titanium.
 7. The microelectronicstructure according to claim 1, wherein said noble metal is platinum. 8.The microelectronic structure according to claim 1, wherein saidoxygen-bonding additive forms a proportion by weight of said firstconductive layer of between 1% and 10%.
 9. A method for producing amicroelectronic structure, which comprises the steps of: preparing asubstrate; simultaneously applying a basic material and a oxygen-bondingadditive to the substrate to form a first conductive layer, theoxygen-bonding additive containing at least one element selected fromthe group consisting of Group IVb elements and lanthanum group elements;depositing a second conductive layer onto the first conductive layer,the second conductive layer containing a noble metal; and applying ametal oxide dielectric to the second conductive layer.
 10. The methodaccording to claim 9, which comprises applying the basic material andthe oxygen-bonding additive to the substrate by a physical sputteringmethod using a common source.
 11. The method according to claim 9,wherein the basic material is formed from a noble metal selected fromthe group consisting of platinum, palladium, rhodium, iridium,ruthenium, osmium, rhenium, a conductive oxide of the abovementionedmetals, and a mixture of the abovementioned compounds and elements. 12.The method according to claim 9, wherein the oxygen-bonding additiveforms a proportion by weight of the first conductive layer of between0.5% and 20%.
 13. The method according to claim 9, wherein theoxygen-bonding additive forms a proportion by weight of the firstconductive layer of between 1% and 10%.
 14. The method according toclaim 9, which comprises using one of zirconium, hafnium, cerium and acombination of zirconium, hafnium and cerium as the oxygen-bondingadditive.
 15. A method of producing a memory circuit, which comprisesthe steps of: forming a microelectronic structure containing: at leastone substrate; a first conductive layer disposed on the substrate, thefirst conductive layer composed of at least one basic material having atleast one oxygen-bonding additive containing at least one elementselected from the group consisting of Group IVb elements and lanthanumgroup elements; a second conductive layer disposed on the firstconductive layer and containing a noble metal; and a metal oxidedielectric at least partially covering the second conductive layer;using the microelectronic structure to form a first part of a storagecapacitor, the first conductive layer forming a first capacitorelectrode; and providing a second electrode disposed on the metal oxidedielectric for forming a second part of the storage capacitor.